Ion exchange resins are synthetic, porous organic solids, typically having a polystyrene matrix, acidic or basic groups bonded to the matrix and hydrogen or sodium ions bonded to the acidic or basic groups. They are effective chemical filters for hazardous wastes in contaminated water, for example, which may include radioactive and non-radioactive materials. Polymeric sorbents, such as charcoal, have a charged surface and are also effective chemical filters of such wastes. However, the use of these materials to absorb hazardous wastes presents the problem of the effective disposal of the contaminated ion exchange resins and polymeric sorbents.
U.S. Ser. No. 08/713,243, filed on Sep. 12, 1996, assigned to the assignee of the present invention and incorporated by reference, herein, discloses a process for the immobilization of radioactive and other hazardous wastes with ferric oxides such as ferrihydrite. It was demonstrated that ion exchange resins and polymeric sorbents, and other contaminated materials, may be effectively immobilized by mixing the contaminated resin or sorbent with hydrated ferric oxide comprising at least 20% Fe.sub.2 O.sub.3, by dry weight of the total weight of the mixture. The mixture was pressed at temperatures of about 260.degree. C. A large part of the water was removed while the mixture was under pressure of 70,000 psi for a period of time to produce a solid composition containing the contaminated material. Such a mixture was successfully consolidated at a pressure of 25,000 psi, with the addition of additives such as metallic fines. Prior to mixing with the hydrated ferric oxide, the ion exchange resin or polymeric sorbent was dried by heating, as well as ground to reduce its particle size. In the Examples, the cation ion exchange resin was dried at 120.degree. C. while the polymeric sorbent was dried at 118.degree. C.
Volume reduction is an important economic consideration in hazardous waste disposal because the volume of the waste to be disposed is a significant factor in the burial cost. The pressure and temperature of a disposal process are also important economic considerations because of their impact on processing costs. In U.S. Ser. No. 08/713,243, volume reductions of up to 10 times for ion exchange resins were achieved by pressing at 70,000 psi and 260.degree. C. The volume of the ion exchange resins and polymeric sorbents immobilized for disposal in accordance with U.S. Ser. No. 08/713,243 could be further decreased by preheating the resin or sorbents at higher temperatures. However, thermal processing of organic solids tends to proceed in an uneven manner, resulting in local hot spots of material. Such hot spots can cause local eruptions and popping in the sample, and enhance the emission of hazardous organic compounds, such as the products of incomplete combustion ("PICs"). Such emissions create serious health risks. Heating ion exchange resins in particular causes the loss of sorbed volatiles and moisture followed by partial decomposition of the resin itself and further volatilization. Cation exchange resins are stable up to about 120.degree. C., while anion exchange resins are stable only up to about 60.degree. C.
Incineration and thermal decomposition have also been proposed for the immobilization and volume reduction of hazardous wastes. Incineration, for example, is discussed in "Incineration of Ion-Exchange Resins in a Fluidized Bed", Valkiainen, et al., Nuclear Technology, Vol. 58, August 1982, pp. 248-255; and "Incineration of Ion-Exchange Resins Using a Cocentric Burner", Chino et al., Transactions of the American Nuclear Society, 44, (1983), pp. 434-435. However, when processed at sufficiently high temperatures to cause decomposition in an aerated or oxygenated environment, which is typical in incineration and thermal decomposition processes, ion exchange resins and polymer sorbents undergo the same thermal instabilities discussed above. Similarly, disposal procedures including heat treatments for other organic polymers and plastics, which form a large part of the solid wastes generated by human activity, present such problems.
Vitrification is another disposal technique, wherein the waste material is mixed with metal oxide, such as sodium oxide, calcium oxide or boron oxide, and silica at temperatures over 800.degree. C. to form a glass for immobilizing the residues of the waste material. Because of the high temperatures involved, vitrification is an expensive, complex procedure.
It would be advantageous to avoid the thermal instabilities caused by high temperature processing of organic materials in aerated or oxygenated environments. It would also be advantageous to decrease the pressures and temperatures used in waste disposal processes.